This invention relates to a catheter-based system to position an electrode for providing energy to a biological site, and more particularly, to a catheter having an expandable distal end configured to maintain a desired spacing between bipolar electrodes.
The venous system of the lower limb consists essentially of the superficial venous system and the deep venous system with perforating veins connecting the two systems. The superficial system includes the long or great saphenous vein and the short saphenous vein. The deep venous system includes the anterior and posterior tibial veins which unite to form the popliteal vein, which in turn becomes the femoral vein when joined by the short saphenous vein.
Veins are hollow anatomical structures which contain numerous one-way valves for directing blood flow back to the heart. The venous valves prevenrograde flow as blood is pushed forward through the vein lumen and back to the heart. Each cusp of bicuspid venous valves form a sack or reservoir for blood which, under pressure, forces the free surfaces of the cusps together to prevent retrograde flow of the blood and allow antegrade flow to the heart. When an incompetent valve is in the flow path of retrograde flow toward the foot, the valve is unable to close because the cusps do not form a proper seal and retrograde flow of blood cannot be stopped.
Incompetent valves in the venous system can occur with vein dilation. Separation of the cusps of the venous valve at the commissure may occur as a result. The leaflets are stretched by the dilation of the vein and concomitant increase in the vein diameter which the leaflets traverse. Stretching of the leaflets of the venous valve allows the loose leaflets to fold on themselves and leave the valve open. This prolapse can allow reflux of blood in the vein. Eventually the venous valve fails, thereby increasing the pressure on the lower venous sections and overlying tissues. Two venous diseases which often involve vein dilation are varicose veins and chronic venous insufficiency.
The varicose vein condition includes dilation of the veins of the lower limb, resulting in unsightly discoloration, pain and ulceration. Varicose veins often involve incompetence of one or more venous valves, which allow reflux of blood from the deep venous system to the superficial venous system or reflux within the superficial system. Current treatments include such invasive open surgical procedures as vein stripping, sclerotherapy, and occasionally, vein grafting, venous valvuloplasty, and the implantation of various prosthetic devices. The removal of varicose veins from the body can be a tedious, time-consuming procedure having a painful and slow healing process. Complications, scarring, and the loss of the vein for future cardiac and other by-pass procedures may also result. Along with the complications and risks of invasive open surgery, varicose veins may persist or reoccur, particularly when the valvular problem is not corrected. Due to the long and tedious nature of the surgical procedure, treating multiple venous sections can exceed the physical stamina of the physician, and thus render complete treatment of the varicose vein conditions impractical.
As the veins dilate due to increased pressure, the valves in the veins fail. This causes the pressure to increase on the next valve and vein segment down, causing those veins to dilate, and as this continues, the valves in the veins eventually all fail. As they fail, the effective height of the column of blood above the feet and ankles grows, and the weight and hydrostatic pressure increases. When the weight of that column reaches a critical point from the valve failures, ulcerations of the ankle begin to form. These ulcerations do not heal easily because the weight of blood which caused them continues to persist.
The ligation of vascular lumen by cauterization or coagulation using electrical energy from an electrode has been employed as an alternative to the surgical removal of such veins. However, ligation procedures close off the lumen, essentially destroying their functional capability. For example, it is known to introduce an electrode into the leg of a patient, and position the electrode adjacent the exterior of the varicose veins to be treated. Through a small stab incision, a probe is forced through the subcutaneous layer between the fascia and the skin, and then to the various veins to be destroyed. Electrodes at the outer end of the probe are placed adjacent the varicose veins. Once properly positioned, an alternating current of about 500 kilohertz is applied to destroy the adjacent varicose veins. Such veins are no longer capable of allowing blood to flow through, and are no longer of use. For example, ligating the saphenous vein would render that vein unavailable for harvesting in other surgical procedures such as coronary by-pass operations. Ligation techniques which functionally destroy the vein lumen would appear be inappropriate to a corrective procedure for restoring and maintaining the function of the vein.
Electrode catheters having longitudinal arms circumferentially spaced on the catheter, with electrodes of opposite polarity being located on adjacent arms, can produce an RF field around the . The longitudinal arms can be expanded away from the catheter. As the longitudinal arms are expanded radially away from the catheter, the space between the electrodes on the arms increase. RF field would be,weaker as the longitudinal arms are expanded away from the catheter, and stronger as the arms are brought closer to the catheter. Thus, the heating effect from the field generated by the electrodes would vary during the procedure. A more constant field generated during the procedure should allow for a more predicable heating effect.
Hence, those skilled in the art have recognized a need for an expandable catheter system that maintains the same bipolar electrode spacing regardless of the degree of expansion of the catheter for a more predictable heating effect. Those skilled in the art also recognize a need for a less expensive expandable catheter in addition to one that can be more easily manufactured.